Appendix. 

 (Added Jan. 1. 1907.) 



Since the above was written, considerable doubt bas arisen in our 

 minds as to the real nature and significance of what we have described 

 as „Bathy chrome tissue". In some cases, we find on looking over our 

 slides again, the appearances are very striking, and suggest very 

 strongly a special kind of tissue, as distinct from the ordinary zymo- 

 genous as is that of the ordinary „Islet of Langerhans"; this is spe- 

 cially the case in the pancreas of the pigeon after inanition. But in 

 other cases the aspect of the dark columns is not so convincing, and 

 appears rather as if due to some adventitious circumstance, as, for 

 example, some irregular or uneven action of the fixing or staining 

 agents. 



The points which seem to be adverse to the view that we are 

 dealing with a special and distinct kind of tissue are as follows: 1. The 

 appearances are not of constant occurrence, and it is difficult to lay 

 down any rule as to what part of the gland may be expected to 

 contain it. 2. It seldom if ever, is found in its typical condition, except 

 near the periphery of a section. 



Then, again, we suspect that we have classed together more than 

 one structure under a common name. Thus, it seems to us very doubt- 

 ful whether the individual „bathychrome" cells of the mammalian pan- 

 creas have really anything in common, except the deeply- staining 

 reaction, with the striking dark-staining masses and columns depicted 

 in Pi. iV, fig. 7 and i)late V, fig. 12, for the pigeon. 



It certainly cannot be due to any irregularity in the action of 

 the staining fluid, for it can be traced in serial sections, and its form 

 definitely ascertained. Nor have we been able to imagine, nor has 

 anyone, l)een able to suggest to us, how any of oui' fixing fluids could 



