116 



a unique role in the metabolism of Pfeiffer's bacillus, but are 

 just as important for the growth of the majority of other 

 common bacteria. Ordinary peptone-broth (partly also pep- 

 tone or broth alone) contains these substances. 



(2) A body .,X" (or perhaps better, a group of bodies, 

 which resemble one another as far as they interest us here), 

 which is principally found in haemoglobin and several of its 

 derivatives, and is characterised by possessing the same „oxygen 

 conducting power' 1- as haemoglobin and by resisting heating 

 to 120' for a short time (3/ 4 hour is named). 



(3) A body „V' - which occurs very widely distributed in 

 the animal and vegetable kingdom: bacteria, yeast cells, carrots, 

 tomatoes, beans, muscle, spleen, liver, kidney, and so forth. 

 Serum and serous fluids may be slightly active. In the case 

 of ascitic fluid, according to Davis (6), this only happened 

 when it had a high specific gravity and was fresh. Perhaps 

 however the activity is due in the last case to the content of 

 substances derived from blood corpuscles (Thjotta & Avery 

 (1)). It is much less thermostabile than „X", as it is more or 

 less quickly destroyed at 100° and instantaneously at 120°. (The 

 signs „X k ' and „V" are those used by Thjotta & Avery). 



We will assume that we always use the same medium (pep- 

 tone-broth agar containing the substances referred to under 

 the heading (1) in sufficient quantity) and add to it substances 

 which will furnish it with the growth factors „X" and „V'\ 

 It will then be seen that we can attain the same maximal 

 1 i m i t of growth for Pfeiffer's bacillus by several different 

 ways. We can imagine that for this maximal growth a definite 

 concentration of ,X" and also of „V" is required in all cases. 

 If there is more of one or both factors, the surplus is useless. 

 If we add to the medium a mixture of „X" and „V" which 

 is inadequate to produce maximal growth, two possibilities will 

 arise: (1; „X" is in excess. (2) „V" is in excess. (We set 

 aside the special case when they are present in „equivalenl u 

 amounts). In the first case the addition of „V" only (that is 

 to say without „X") will increase the growth, in the second 

 case it will be without effect. 



An attempt will now be made to give an account of the 

 conditions of growth of Pfeiffer's bacillus under different cir- 

 cumstances, on the basis of the above scheme. It will then 



