2 VETERINARY PHYSIOLOGY 



fluid interstitial part. In all protoplasm, therefore, there seems 

 to be a certain amount of organisation, and in certain cells this 

 organisation becomes very marked indeed. 



II. Physiology. A knowledge of the essentials of the physi- 

 ology of protoplasm may be gained by studying the vital 

 manifestations of one of the simplest of living things, the yeast 

 plant (Saccharomyces Cerevisae). 



This plant consists of very minute oval or spherical bodies 

 frequently connected to form chains, each composed of a harder 

 outer covering or capsule and of a softer inner substance which 

 has all the characters of protoplasm. 



Its physiology may be studied by placing a few torulse in a 

 solution, containing glucose, C 6 H 12 6 , and urea, CON 2 H 4 , with 

 traces of phosphate of soda, Na 2 HP0 4 , and sulphate of potash, 

 K 2 S0 4 . 



If the vessel be kept all night in a warm place the clear 

 solution will in the morning be seen to be turbid. An 

 examination of a drop of the fluid shows that the turbidity is 

 due to the presence of myriads of torulse. In a few hours the 

 few torulse placed in the fluid have increased many hundred- 

 fold. The whole mass of yeast has grown in amount by the 

 growth and multiplication of the individual units. 



This power of growth and reproduction under suitable con- 

 ditions is the essential characteristic of living matter. 



What are the conditions necessary for the manifestation of 

 these phenomena of life ? 



1. If the yeast be mixed with the solid constituents of the 

 solution in a dry state no growth or reproduction occurs. 



Water is essential. 



2. If the yeast, mixed with the solution, be kept at the 

 freezing point no growth takes place, but this proceeds actively 

 at about 36 C. A certain temperature is necessary for the 

 vitality of protoplasm. In the absence of these conditions, proto- 

 plasm is only potentially alive, and in this state it may remain 

 for long periods without undergoing any change, as in the seeds 

 of plants and in dried bacteria. 



The conditions essential for the manifestations of life being 

 present, in order that the growth of the yeast may take place, 

 there must be : 



