ATROPHY OF THE ORGANS OF THE LARVAL FROG. 159 



the difference is significant. There are two substrates present in 

 this system, namely, blood-serum proteins and secondly the tissue 

 from the tail. The conclusion is warranted that there is a dif- 

 ference in enzyme content between the atrophying and the normal 

 tissue. Granting that the serum proteins are more readily 

 digested by the enzymes of the tail issue, we are still driven to 

 assume that the enzymes are different in the two cases. 



We have seen, then, that correlative with histological dif- 

 ferences, there are enzyme differences in the case of atrophying 

 and non-atrophying material. 



It is possible that the experiments described in the preceding 

 paragraphs do not bear critically upon the problem as to what 

 induces atrophy of the metamorphosing larva. It may be urged 

 that phagocytes could be operative in each of these cases. To 

 assume this, it would be necessary to demonstrate that within 

 the relatively short period of 24 hours, phagocytes, working in 

 vitro, could perform the task of digesting the tissue in the amounts 

 given. We should at once seek to answer the question as to 

 whether a marked increase of phagocytes is to be observed in 

 atrophying material over the normal. The writer (20) has made 

 differential counts of the blood cells of normal and involuting 

 individuals with the result that no increase commensurate with 

 the difference in digesting power in the two cases exists. That 

 there is a concentration of phagocytes (polynuclear leucocytes) 

 in the affected areas is evident from Fig. I , given above, and also 

 from the work of Mercier; the actual number, however, remains 



the same. 



THE CAUSES INDUCING ATROPHV. 



Mammalian experiments at the hands of Martin Jacoby and 

 many other investigators have shown that atrophy involving 

 autolysis is induced when the blood supply is interfered with. 

 It is not necessary to occlude the supply directly; interruption of 

 the blood supply will serve to cause atrophy. Bataillon (21) 

 found that in the frog, the development of the pygostyle caused 

 a change in the distribution of the blood supply throughout the 

 tail. This does not involve complete occlusion, for Mercier found 

 that, comparatively late in metamorphosis, phagocytes bearing 

 carmin granules picked up from the dorsal lymph sac into which 



