384 NATURAL SCIENCE. May, 



are produced and the animal may die. The epithelial cells of the 

 alimentary canal protect us from these poisonous effects by turning 

 back into insoluble proteids the peptones they absorb. Again, sugar 

 injected into the blood passes into the lymph, but soon the percentage 

 in the lymph is higher than the percentage in the blood — a result 

 which cannot be explained by filtration or diffusion, and must be due 

 to the "secretory activity" of the cells of the vessel walls. Even 

 the vital action of the cells of the intestine does not alone perform 

 the work of digestion. The process is aided by multitudes of bacteria 

 that thrive where the antiseptic gastric juice has deen neutralised by 

 the fluid from the pancreas. 



Another striking " vitalistic " occurrence is the excretion of car- 

 bonic acid by the lungs. The tension of carbonic acid in the air in 

 the alveoli of the lungs is much lower than the tension of carbonic acid 

 in the veins. Hence it seems a simple physical process that carbonic 

 "acid should pass from the veins to the alveolar air. But the process 

 goes on so far that when the venous blood has become arterial, the 

 tension of the carbonic acid is lower in the blood than in the alveolar 

 air. Here again secretory activity of the epithelium lining the 

 pulmonary alveoli is called into account. 



Some of the other changes from the physiological chemistry of 

 our youth are equally striking. Thus, a large number of the so-called 

 chemical processes depend on unorganised ferments ; that is to say, 

 on ferments possessing the characters of living things, except that 

 they cannot be identified as separate organisms having shape, size, 

 and so forth. Of these, some we know, others are more recent dis- 

 coveries. Ptyalin of the saliva, pepsin and rennet of the stomach, 

 trypsin, amylopsin, and steapsin of the pancreas, and the fibrin 

 ferment in the white blood corpuscles, all are appeals from chemistry 

 to vital action. 



The organs and tissues of the body are bound together in much 

 more than a mechanical fashion. Experimental evidence has shown 

 that, in addition to its own special functions, each organ contributes in 

 a vague way to the " general metabolism of the body." The expres- 

 sion of the fact is vague, but the fact is real and striking. Extirpa- 

 tion of the testes causes many well-known general changes in addition 

 to the special change of impotency. And so extirpation of other 

 organs brings about many general changes over the whole body in 

 addition to loss of the special. 



The special functions of organs are not the simple occurrences 

 formerly believed in. For instance, urea is not formed in the kidneys, 

 not even in the muscles, but in the liver ; while, on the other hand, 

 bile is not a digestive fluid but probably purely excretory. 



We advise strongly those who are working in other branches of 

 Biology to read Dr. Halliburton's clear and interesting little book. 

 Many problems await their solution by the joint action of morphological 

 and physiological considerations, and we recommend morphologists 

 in particular to notice the paths along which the students of function 

 are travelling. 



It remains to be said that from the point of view of students 

 Dr. Halliburton's book is admirable. The directions for practical 

 work at the beginning of each section are explicit and simple ; even 

 dull students should require little further direction. The descriptions 

 of apparatus are very clear, and if they are studied not directly from 

 the figures in the book but with the apparatus in the laboratory, 

 much time will be saved from the teaching of physics for the teaching 

 of physiology. 



