TRUE POSITION OF VETERINARY SCIENCE. 
311 
life occurs without the incessant repetition of these changes, hence 
it is evidently necessary to know what they are, and how they 
are produced. An acquaintance with the laws of chemistry and 
of physics must therefore underlie all study of vital manifesta¬ 
tions. 
A few illustrations would perhaps show this most clearly, and 
point out the intimate relations and dependencies that exist be¬ 
tween these sciences and the science of life. Of what, for 
instance, does the whole process of nutrition consist ? It is from 
beginning to end composed of a definite series of chemical phe¬ 
nomena. The body is a sort of laboratory supplied with all the 
various reagents for solution, analysis, combination and decom¬ 
position ; with crucibles, retorts, and furnaces in which these oper¬ 
ations are conducted. The study of digestion in the higher 
animals is almost entirely a study of chemical changes. The 
food that is ingested cannot be appropriated directly, but must 
undergo certain modifications before it can be absorbed and be- 
come a part of the body. The starchy foods are, from their 
nature, insoluble. They are first converted into sugar by the 
salivary and pancreatic ferments, and when thus altered are dis¬ 
solved and absorbed by the blood vessels. Albumen is insoluble. 
When it comes in contact with the gastric juice which is poured 
into the stomach, it is converted bv the pepsine of that fluid into 
albuminose or peptone, and is then ready for absorption. When 
these substances are circulating in the blood they meet with 
oxygen, which has likewise reached the body from an external 
source, and there a process of oxidation takes place, resulting in 
the production of heat and energy, just as oxidation outside the 
body causes the same effects. 
The laws of physics bear a no less close and demonstrable 
relation. The conversion of liquid water into vapor by means of 
heat is one example. How otherwise could we explain the 
evaporation of water from the surface of the, body in the form of 
perspiration ? The process of respiration is another instance. 
The diaphragm and intercostal muscles contract, and together 
expand the cavity of the thorax; then, on account of the atmos¬ 
pheric pressure, the air must enter the space which else would.be 
