634 



SCIENCE. 



[N. S. Vol. XXII. No. 568. 



plants upon bacteria for keeping up the store 

 of carbon dioxide and of combined nitrogen 

 necessary for plant life, and bacteria depend- 

 ent upon animal or vegetable matter for their 

 nourishment. The very important and benefi- 

 cent role here played by bacteria in the house- 

 hold of nature has led to the view that they 

 also hold a similar relation to the human 

 body directly, and that the myriads of bac- 

 teria found in the alimentary canal not only 

 serve as aids to digestion, but are absolutely 

 essential to this process. 



This view was placed upon a scientific basis 

 by Schottelius, who sterilized hens' eggs, 

 hatched them in sterilized incubators and fed 

 them on sterilized food to find that they ate 

 voraciously, but instead of increasing in 

 weight, gradually grew thinner and died in 

 the second or third week. If, however, hen 

 manure was added to the food before the 

 chicks had succumbed, they soon revived and 

 developed rapidly and normally. This ex- 

 periment proves that bacteria as a matter of 

 fact are necessary to digestion in the case of 

 chicks. It does not follow, however, that the 

 same is true of human beings or of mammalia 

 in general. Thierfelder and ISTuttall found 

 that guinea-pigs, taken aseptically from the 

 mother and fed aseptically, developed perfectly 

 normally; this experiment was carried on, 

 however, but for a few days. 



There are many other reasons for doubting 

 the usefulness of bacteria as aids to digestion 

 in the human being: 



1. The ferments of the alimentary juices 

 ptyalin, pepsin, trypsin, pancreatin, etc.) are 

 capable of carrying on digestion without the 

 aid of bacteria. 



2. Digestion by bacteria in the stomach is 

 impossible under normal conditions, on ac- 

 count of the acid reaction of its contents. 



3. It is a question whether the bacteria of 

 the intestines, being bathed in foodstuffs 

 already digested do not in a great measure 

 lose the power of peptonizing albuminous sub- 

 stances just as nitrogen-fixing bacteria culti- 

 vated on media rich in nitrogen lose the power 

 of fixing nitrogen from the air. 



4. By far* the great majority of bacteria 

 are found in the large intestines, whereas the 



digestion arid absorption of food take place 

 almost solely in the small intestines. Metch-' 

 nikofi emphasizes this point in particular and 

 maintains that the large intestines are not 

 only useless, but positively harmful, and even 

 suggests the idea of removing them surgically. 



5. Digestion by bacteria is accompanied by 

 the production of substances which are poison- 

 ous to the animal body and, for instance, eggs, 

 meat, fish, oysters, etc., undergoing bacteritic 

 digestion (putrefaction) are absolutely unfit 

 for use and in some cases violently poisonous. 

 This fact tallies also with practical experience, 

 which teaches us that wherever bacteria obtain 

 the upper hand and the normal process of di- 

 gestion is replaced by bacteritic action, either 

 in the stomach or intestines, serious disturb- 

 ances in the shape of ' spoiled stomach,' head- 

 ache, nausea, vomiting, diarrhoea, etc., take 

 place. 



In the mouth most of the bacteria convert 

 the carbohydrates into lactic and other acids 

 which decalcify the enamel and dentine, so 

 causing decay of the teeth and all its accom- 

 panying evils, and we have no evidence 

 whatever that the physiological action of the 

 saliva is furthered by them, in a correspond- 

 ing degree. 



Bacteria are consequently not only not es- 

 sential to digestion, but they produce serious 

 disturbances in the mouth, stomach and in- 

 testines wherever they multiply in excessive 

 numbers. They should consequently be kept 

 down by every means at our disposition and 

 especially as to the mouth; a thorough cleans- 

 ing of the teeth after every meal not only 

 goes far- to keep the teeth and gums in a 

 healthy condition, but contributes much to 

 the general health. 



There are, however, in the various cavities 

 of the human body communicating with the 

 outer world (mouth, intestines, vagina) cer- 

 tain bacteria which constitute the peculiar 

 florae of these cavities and which serve a bene- 

 ficial purpose by their antagonism to other 

 bacteria. 



Some thirty lantern views illustrated the 

 general subject and the speaker's own re- 

 searches on the bacteria of the mouth; there 

 were several beautifully stained sections of 



