BACTERIA AND SMELLS 189 



An important fact about animal smells is that many 

 which we might be inclined to attribute to the animal 

 which diffuses them, are really due to the fermentative or 

 putrefactive action of bacteria which swarm on the skin 

 and in the intestines of animals. It is often difficult to 

 decide how far a peculiar animal odour is due directly to 

 a substance secreted by the animal, and how far the odour 

 of that substance is modified or even entirely produced by 

 the chemical changes set up in secretions of the body- 

 surface by bacteria. Several distinct repulsive smells 

 liable to occur on the human body are due to want of 

 cleanliness in destroying bacteria by proper antiseptics. 

 The fatty and waxy secretions of the skin are often 

 decomposed by bacteria, even before complete extrusion 

 from the glands in which they are formed, whilst the 

 decomposition of food in the mouth and intestines by 

 bacteria alters materially both the natural odour of the 

 animal's breath and the smell of the intestinal con- 

 tents. In young and healthy animals in natural conditions 

 there is some check it is not easy to say what 

 upon the putrefactive activities of the omnipresent bacteria. 

 The skin of a healthy young animal has a pleasant odour, 

 and its breath (notably in the case of the cow and the 

 giraffe) is naturally sweet-smelling. The same should be 

 the case, under perfectly healthy conditions, with human 

 beings. 



There is one important cause of animal odours and 

 flavours upon which I have not hitherto touched. Many 

 animals acquire an odour or flavour directly from the food 

 upon which they feed. Certain odorous bodies are in the 

 food and are taken up into the blood of the consuming 

 animal unchanged, and are then thrown out by secreting 

 glands on the skin. This is the case with the odorous 

 substance of onions. People do not smell of onions after 

 they have eaten them in conseqence of particles of onion 



