GASTRIC CECA OF THE HETEROPTERA. 147 



tional cases, when they may assume the role of active parasites. 

 Others hold, on the contrary, that their presence is of very great 

 importance in the overgrowing and destroying of the occasional 

 invader, which if allowed to develop unchecked might seriously 

 injure the host, and also in the inhibitory action which they exert 

 upon the common putrefactive intestinal bacteria; while still 

 others assert that, in addition to the function just mentioned, 

 these bacteria not only play an important part in, but are abso- 

 lutely essential to proper digestion, at least in the higher animals. 



The first serious attempt to determine by actual experiment 

 the part played by intestinal bacteria in digestion appears to have 

 been made by Nuttall and Thierfelder in their classical experi- 

 ments with guinea pigs. In these experiments the young animals 

 were removed from the mother by Csesarian section and trans- 

 ferred at once to ingeniously constructed cages where they were 

 kept under absolutely aseptic conditions and supplied with 

 sterile food and water. Under these conditions the authors were 

 able to keep the animals alive for ten days, at the end of which 

 time they were found to have increased considerably in weight. 

 Of the four animals carried through the experiment the increase 

 in weight was found to be 5.5, 14, 16 and 28 grams respectively. 



From their data the authors conclude that intestinal bacteria 

 are not essential to digestion and their results have been widely 

 quoted by physiologists as showing that the intestinal bacteria 

 are at most of only minor importance in this process. 



The results of these experiments are far from being conclusive, 

 as has frequently been pointed out. Thus, Schottelius was able 

 to keep newborn guinea pigs alive for ten days by giving them 

 nothing but sterile water. The same author also found that the 

 intestinal contents of a normal ten-days-old guinea pig weighed 

 from twelve to fifteen grams, and in this case the intestine was 

 not completely filled; while Nuttall and Thierfelder, upon 

 examining the pigs at the conclusion of their experiments, found 

 that the colon and especially the csecum were crammed full, and 

 even greatly distended, with a brown caseous material. Schot- 

 telius insists that this constantly accumulating mass of undigested 

 food in the intestine would much more than account for the 

 increase in weight reported by Nuttall and Thierfelder and that, 



