Preliminary remarks on immunity in animal kingdom 65 



pancreatic function is carefully regulated as regards its adaptation to 

 the characters of the food substances on which it is to act Such 

 adaptation may even become permanent. 



Whilst, as already stated, the stomach, under the influence of a fixed 

 diet, is incapable of effecting any lasting modification in the composition 

 of its secreted juice, the pancreas may reach this degree of perfection. 

 When a dog is fed for several weeks on bread or on milk and is then 

 placed on flesh diet its pancreatic juice is found to become progres- 

 sively richer in trypsin. Whilst this augmentation of the proteolytic 

 power is being brought about, the juice becomes poorer and poorer in 

 amylase. Wassilieff x has carried out a large number of experiments 

 on this point and has demonstrated a very remarkable adaptation 

 of the pancreatic juice to the wants of nutrition, an adaptation that 

 may become permanent. A dog which has been accustomed to digest 

 bread and milk adapts itself to this nourishment : its pancreatic juice 

 contains less and less trypsin, but, on the other hand, becomes richer 

 in amylase. Pawloff observed that in dogs great variations in the 

 composition of the pancreatic juice are often present ; this he attributes 

 to the diet to which these animals had been previously subjected. 



Not only does the quality of the digestive juices accommodate itself 

 to the wants of digestion ; their quantity also undergoes variations 

 according to the part that these juices have to play. Thus, Pawloff 

 has observed that his dogs secreted a saliva which was very fluid and 

 very abundant when he gave them acids, bitter substances or other sub- [70] 

 stances they did not like. On the other hand, the presence of food in 

 the mouth, or even the sight of it, excited the secretion of a thick saliva 

 containing a large quantity of mucin. In the first case the part played 

 by the saliva was that of diluting the injurious substances as much as 

 possible, in the second that of facilitating the deglutition of the food. 



In general the organism manifests a tendency to produce more 

 digestive ferments than it actually needs for digestion. It is for this 

 reason probably that they are often found outside the digestive canal. 

 Among these ferments pepsin and amylase, especially, have been 

 definitely proved to be present in the urine of man and of some 

 mammals, notably the dog. The data as to rennet and trypsin are 

 not so well established. But, as several of these ferments, such as 

 amylase and trypsin, may be derived from several sources in the 

 organism, their elimination by the urine is less important for the 

 thesis I have just formulated than is that of pepsin. 



1 Arch. d. sc. biol., St.-Petersb., 1893, t. n, p. 219. 

 B. 5 



