A History of Science, vol 4, Henry Smith Williams [best books to read in life txt] 📗

whom the

principle meant so much and in whose hands it extended so far.

 

Of course this entire principle, in its broad outlines, is

something with which every student of anatomy had been familiar

from the time when anatomy was first studied, but the full

expression of the “law of co-ordination,” as Cuvier called it,

had never been explicitly made before; and, notwithstanding its

seeming obviousness, the exposition which Cuvier made of it in

the introduction to his classical work on comparative anatomy,

which was published during the first decade of the nineteenth

century, ranks as a great discovery. It is one of those

generalizations which serve as guideposts to other discoveries.

BICHAT AND THE BODILY TISSUES

Much the same thing may be said of another generalization

regarding the animal body, which the brilliant young French

physician Marie Francois Bichat made in calling attention to the

fact that each vertebrate organism, including man, has really two

quite different sets of organs—one set under volitional control,

and serving the end of locomotion, the other removed from

volitional control, and serving the ends of the “vital processes”

of digestion, assimilation, and the like. He called these sets of

organs the animal system and the organic system, respectively.

The division thus pointed out was not quite new, for Grimaud,

professor of physiology in the University of Montpellier, had

earlier made what was substantially the same classification of

the functions into “internal or digestive and external or

locomotive”; but it was Bichat’s exposition that gave currency to

the idea.

 

Far more important, however, was another classification which

Bichat put forward in his work on anatomy, published just at the

beginning of the last century. This was the division of all

animal structures into what Bichat called tissues, and the

pointing out that there are really only a few kinds of these in

the body, making up all the diverse organs. Thus muscular organs

form one system; membranous organs another; glandular organs a

third; the vascular mechanism a fourth, and so on. The

distinction is so obvious that it seems rather difficult to

conceive that it could have been overlooked by the earliest

anatomists; but, in point of fact, it is only obvious because now

it has been familiarly taught for almost a century. It had never

been given explicit expression before the time of Bichat, though

it is said that Bichat himself was somewhat indebted for it to

his master, Desault, and to the famous alienist Pinel.

 

However that may be, it is certain that all subsequent anatomists

have found Bichat’s classification of the tissues of the utmost

value in their studies of the animal functions. Subsequent

advances were to show that the distinction between the various

tissues is not really so fundamental as Bichat supposed, but that

takes nothing from the practical value of the famous

classification.

 

It was but a step from this scientific classification of tissues

to a similar classification of the diseases affecting them, and

this was one of the greatest steps towards placing medicine on

the plane of an exact science. This subject of these branches

completely fascinated Bichat, and he exclaimed, enthusiastically:

“Take away some fevers and nervous trouble, and all else belongs

to the kingdom of pathological anatomy.” But out of this

enthusiasm came great results. Bichat practised as he preached,

and, believing that it was only possible to understand disease by

observing the symptoms carefully at the bedside, and, if the

disease terminated fatally, by post-mortem examination, he was so

arduous in his pursuit of knowledge that within a period of less

than six months he had made over six hundred autopsies—a record

that has seldom, if ever, been equalled. Nor were his efforts

fruitless, as a single example will suffice to show. By his

examinations he was able to prove that diseases of the chest,

which had formerly been classed under the indefinite name

“peripneumonia,” might involve three different structures, the

pleural sac covering the lungs, the lung itself, and the

bronchial tubes, the diseases affecting these organs being known

respectively as pleuritis, pneumonia, and bronchitis, each one

differing from the others as to prognosis and treatment. The

advantage of such an exact classification needs no demonstration.

LISTER AND THE PERFECTED MICROSCOPE

At the same time when these broad macroscopical distinctions were

being drawn there were other workers who were striving to go even

deeper into the intricacies of the animal mechanism with the aid

of the microscope. This undertaking, however, was beset with

very great optical difficulties, and for a long time little

advance was made upon the work of preceding generations. Two

great optical barriers, known technically as spherical and

chromatic aberration—the one due to a failure of the rays of

light to fall all in one plane when focalized through a lens, the

other due to the dispersive action of the lens in breaking the

white light into prismatic colors—confronted the makers of

microscopic lenses, and seemed all but insuperable. The making of

achromatic lenses for telescopes had been accomplished, it is

true, by Dolland in the previous century, by the union of lenses

of crown glass with those of flint glass, these two materials

having different indices of refraction and dispersion. But, aside

from the mechanical difficulties which arise when the lens is of

the minute dimensions required for use with the microscope, other

perplexities are introduced by the fact that the use of a wide

pencil of light is a desideratum, in order to gain sufficient

illumination when large magnification is to be secured.

 

In the attempt to overcome those difficulties, the foremost

physical philosophers of the time came to the aid of the best

opticians. Very early in the century, Dr. (afterwards Sir David)

Brewster, the renowned Scotch physicist, suggested that certain

advantages might accrue from the use of such gems as have high

refractive and low dispersive indices, in place of lenses made of

glass. Accordingly lenses were made of diamond, of sapphire, and

so on, and with some measure of success. But in 1812 a much more

important innovation was introduced by Dr. William Hyde

Wollaston, one of the greatest and most versatile, and, since the

death of Cavendish, by far the most eccentric of English natural

philosophers. This was the suggestion to use two plano-convex

lenses, placed at a prescribed distance apart, in lieu of the

single double-convex lens generally used. This combination

largely overcame the spherical aberration, and it gained

immediate fame as the “Wollaston doublet.”

 

To obviate loss of light in such a doublet from increase of

reflecting surfaces, Dr. Brewster suggested filling the

interspace between the two lenses with a cement having the same

index of refraction as the lenses themselves—an improvement of

manifest advantage. An improvement yet more important was made by

Dr. Wollaston himself in the introduction of the diaphragm to

limit the field of vision between the lenses, instead of in front

of the anterior lens. A pair of lenses thus equipped Dr.

Wollaston called the periscopic microscope. Dr. Brewster

suggested that in such a lens the same object might be attained

with greater ease by grinding an equatorial groove about a thick

or globular lens and filling the groove with an opaque cement.

This arrangement found much favor, and came subsequently to be

known as a Coddington lens, though Mr. Coddington laid no claim

to being its inventor.

 

Sir John Herschel, another of the very great physicists of the

time, also gave attention to the problem of improving the

microscope, and in 1821 he introduced what was called an

aplanatic combination of lenses, in which, as the name implies,

the spherical aberration was largely done away with. It was

thought that the use of this Herschel aplanatic combination as an

eyepiece, combined with the Wollaston doublet for the objective,

came as near perfection as the compound microscope was likely

soon to come. But in reality the instrument thus constructed,

though doubtless superior to any predecessor, was so defective

that for practical purposes the simple microscope, such as the

doublet or the Coddington, was preferable to the more complicated

one.

 

Many opticians, indeed, quite despaired of ever being able to

make a satisfactory refracting compound microscope, and some of

them had taken up anew Sir Isaac Newton’s suggestion in reference

to a reflecting microscope. In particular, Professor Giovanni

Battista Amici, a very famous mathematician and practical

optician of Modena, succeeded in constructing a reflecting

microscope which was said to be superior to any compound

microscope of the time, though the events of the ensuing years

were destined to rob it of all but historical value. For there

were others, fortunately, who did not despair of the

possibilities of the refracting microscope, and their efforts

were destined before long to be crowned with a degree of success

not even dreamed of by any preceding generation.

 

The man to whom chief credit is due for directing those final

steps that made the compound microscope a practical implement

instead of a scientific toy was the English amateur optician

Joseph Jackson Lister. Combining mathematical knowledge with

mechanical ingenuity, and having the practical aid of the

celebrated optician Tulley, he devised formulae for the

combination of lenses of crown glass with others of flint glass,

so adjusted that the refractive errors of one were corrected or

compensated by the other, with the result of producing lenses of

hitherto unequalled powers of definition; lenses capable of

showing an image highly magnified, yet relatively free from those

distortions and fringes of color that had heretofore been so

disastrous to true interpretation of magnified structures.

 

Lister had begun his studies of the lens in 1824, but it was not

until 1830 that he contributed to the Royal Society the famous

paper detailing his theories and experiments. Soon after this

various continental opticians who had long been working along

similar lines took the matter up, and their expositions, in

particular that of Amici, introduced the improved compound

microscope to the attention of microscopists everywhere. And it

required but the most casual trial to convince the experienced

observers that a new implement of scientific research had been

placed in their hands which carried them a long step nearer the

observation of the intimate physical processes which lie at the

foundation of vital phenomena. For the physiologist this

perfection of the compound microscope had the same significance

that the, discovery of America had for the fifteenth-century

geographers—it promised a veritable world of utterly novel

revelations. Nor was the fulfilment of that promise long delayed.

 

Indeed, so numerous and so important were the discoveries now

made in the realm of minute anatomy that the rise of histology to

the rank of an independent science may be said to date from this

period. Hitherto, ever since the discovery of magnifying-glasses,

there had been here and there a man, such as Leuwenhoek or

Malpighi, gifted with exceptional vision, and perhaps unusually

happy in his conjectures, who made important contributions to the

knowledge of the minute structure of organic tissues; but now of

a sudden it became possible for the veriest tyro to confirm or

refute the laborious observations of these pioneers, while the

skilled observer could step easily beyond the barriers of vision

that hitherto were quite impassable. And so, naturally enough,

the physiologists of the fourth decade of the nineteenth century

rushed as eagerly into the new realm of the microscope as, for

example, their successors of to-day are exploring the realm of

the X-ray.

 

Lister himself, who had become an eager interrogator of the

instrument he had perfected, made many important discoveries, the

most notable being his final settlement of the long-mooted

question as to the true form of the red corpuscles of the human

blood. In reality, as everybody knows nowadays, these are

biconcave disks, but owing to their peculiar figure it is easily

possible to misinterpret the appearances they present when seen

through a poor lens,