EESPIEATION OF BACTERIA 05 



§2. EESPIEATION OF BACTERIA. 



All organisms, animal and vegetable, must respire. To understand 

 what we mean by this, let us consider what happens when we ourselves 

 respire. The protoplasm of our bodies is constantly being broken down 

 into simpler substances, the process resulting in the liberation of a 

 certain amount of energy, which we employ in a variety of ways, as in 

 the warming of our bodies, the repairing of waste tissues, in short, 

 respiration supplies the energy for the continuation of the vital func- 

 tions. The same applies to bacteria, the vast majority of which take 

 up oxygen as we do, in order to effect the decomposition of proto- 

 plasm. Without this absorption of oxygen neither ourselves nor the 

 bacteria (with the exception of a few, the anaerobic bacteria) are able 

 to effect this decomposition. 



Eespiration results in the formation of a large number of sub- 

 stances, as the decomposition of protoplasm does not take place in 

 one but in a series of steps. Of the various substances formed, 

 some are useless and are got rid of. These are the excretion products. 

 Thus in our own case, the carbon dioxide that we exhale from our 

 lungs is such a product. Many of the bacterial excretion products 

 have been identified and some have already been mentioned in a 

 previous chapter. Other substances formed by the decomposition of 

 protoplasm are utilised once more in the building up of protoplasm, 

 which must naturally take place to make up for the loss due to 

 decomposition, and for purposes of growth and multiplication. It 

 will readily be seen that all the general principles which underlie 

 the physiology of the higher animals and plants apply also to 

 bacteria, for like all other organisms, these minute plants are com- 

 posed of protoplasm, which is essentially the same throughout the 

 whole of the animal and vegetable worlds. 



§3. THE FOOD OF BACTERIA. 



In discussing the food of bacteria, it is well to remember that the 

 essential ingredients depend on conditions similar to those which 

 prevail in the case of higher plants and of animals. We must provide 

 those substances which the organism needs for the building up of its 

 own body, and in addition, a number of substances that are not 

 constituents themselves, but which help in the building up of these 



