TRANSACTIONS OF SECTION I. 811 



structure ! TbirJt of all tlie phenomena of karyokinesis, of tiie ckanges in the 

 chromatin that have been observed in cells, of the fibrous structure of the so-called 

 grey matter of the nerve centres, of the complicated appearances seen in nerve 

 cells, and indeed in almost all cells. Then progress has been made in the investiga- 

 tion of the chemical constitution of cells. The new school of what one may call the 

 micro-chemists — and I need only mention the name of Dr. Maccallum, of Toronto, 

 as an example of a worker in this difficult department of science— seems to me to 

 be worthy of the attention of all the younger physiologists. I have a strong 

 belief that a careful investigation of the chemical constitution of cells and of liymg 

 matter, conducted by micro-chemical methods, would be of great value, and might 

 throw some light, not only on the nature of living matter, but on the pathological 

 changes in cells on which disease depends. Morphological examination seems to 

 have been carried nearly as far as it can go ; and here I would mention 

 the morphological examination of malignant tumours, and what is now needed is 

 the detection of those subtle chemical changes that lie far beyond the province of 

 the microscope. 



The conception, however, of the existence in living matter of molecules has not 

 escaped some astute physicists. The subject is discussed with his usual suggestive- 

 ness by Clerk Maxwell in the article Atom in the ' Encyclopfedia Britannica ' in the 

 volume published in 1875, and he places before the physiologist a curious dilemma- 

 After referring to estimates of the diameter of a molecule made by Loschmidt in 

 1865, by Stoney in 1868, and by Lord Kelvin (then Sir W. Thomson) in 1870, 

 Clerk Maxwell writes : — 



' The diameter and the mass of a molecule, as estimated by these methods, are, 

 of course, very small, but by no means infinitely so. About two millions of 

 molecules of hydrogen in a row would occupy a millimetre, and about two 

 hundred million million million of them would weigh a milligramme. These 

 numbers must be considered as exceedingly rough guesses ; they must be corrected 

 by more extensive and accurate experiments as science advances ; but the main 

 result, which appears to be well established, is that the determination of the mass 

 of a molecule is a legitimate object of scientific research, and that this mass is by 

 no means immeasurably small. 



' Loschmidt illustrates these molecular measurements by a comparison with the 

 smallest magnitudes visible bv means of a microscope. Nobert, he tells us, can 

 draw 4,000 lines in the breadth of a millimetre. The intervals between these lines 

 can be observed with a good microscope. A cube, whose side is the 4,000th of a 

 millimetre, may be taken as the minimum visible for observers of the present day. 

 Such a cube would contain from 60 to 100 million molecides of oxygen or of nitro- 

 gen ; but since the molecules of organised substances contain on an average about 

 fifty of the more elementary atoms, we may assume that the smallest organised 

 particle visible under the microscope contains about two million molecules of 

 organic matter. At least half of every living organism consists of water, so that 

 the smallest living being visible under the microscope does not contain more than 

 about a million organic molecules. Some exceedingly simple organism may be 

 supposed built up of not more than a million similar molecules. It is impossible, 

 however, to conceive so small a number sufficient to form a being furnished with a 

 whole system of specialised organs. 



' Thus molecular science sets us face to face with physiological theories. It 

 forbids the physiologist from imagining that structural details of infinitely small 

 dimensions can furnish an explanation of the infinite variety which exists in the 

 properties and functions of the most minute organisms. 



' A microscopic germ is, we know, capable of development into a highly organised 

 animal. Another germ, equally microscopic, becomes when developed an animal of 

 a totally diff"erent kind. Do all the difl!"erences, infinite in number, which distin- 

 guish the one animal from the other arise each from some difference in the structure 

 of the respective germs ? Even if we admit this as possible, we shall be called upon 

 by the advocates of pangenesis to admit still greater marvels. For the micro- 

 scopic germ, according to this theory, is no mere individual but a representative 

 body, containing members collected from every rank of the long-drawn ramification 



