360 GENERAL PHYSIOLOGY 



peutics and prophylaxis of the infectious diseases are based upon this 

 fact, especially the inoculation- and injection-methods of Jenner, 

 Koch, Pasteur, Behring, Roux and others. We know how to 

 produce immunity at will by the artificial introduction of 

 weakened inoculation-substance, of metabolic products of the excit- 

 ant of the disease in question, or of blood-serum from animals that 

 have been exposed to the infection. In all these purely empirical 

 methods of treatment we are totally ignorant of what goes on 

 in the body ; we can only say that the poisoning by the 

 bacterial poisons produces in the cells an after-effect, which can 

 continue in many cases, such as diphtheria, only a relativel}' short 

 time, but in others, such as small-pox, for many years. A phe- 

 nomenon is here presented, the explanation of which is as yet 

 scarcely hinted at. But it is to be expected that cell-physiological 

 researches, which replace with the simplest relations the complex 

 and abstruse conditions presented by human and animal bodies, 

 will be of the greatest service in assisting toward an understandiug. 

 In fact, investigations upon unicellular organisms with various 

 chemical substances have shown that analogous phenomena are to 

 be met with in these forms. Thus, by accustoming Infusoria 

 to weak solutions of corrosive sublimate, Davenport ('96) has made 

 them immune toward solutions of such strength as were at once 

 fatal to non-immunised individuals. Cell-physiological research 

 opens here an uncommonly wide and fruitful field. The system- 

 atic investigation of reactions in the single cell is of fundamental 

 importance not only theoretically, but also for practical medicine.'^ 



3. Tlie, Conduction of the Stimulus 



Inseparably connected with irritability is another property of 

 living substance, viz., the power of conduction of the stim uhis. If a 

 mass of living substance be stimulated localh', as can be done 

 very simply by touching it or pricking it with a fine needle, the 

 reaction is not limited to the point stimulated, but spreads from 

 that place more or less over the neighbouring parts. 



The capacity of conducting the stimulus belongs to all 

 living substance, but in very different degrees. AYhile one kind 

 conducts rapidly and far, another conducts slowlj- and only to 

 the nearest surroundings. 



The capacity of conduction is most pronounced in those forms 

 that are developed exclusively for that purpose, viz., the animal 

 nerve-fibres. Nerves conduct with enormous rapidity and to 

 distances measured by meters. Helmholtz has computed that in 

 a frog's nerve the stimulus is transmitted at a rate of 26 m. per 

 second. In man the rate is still greater, approximately 34 m. in 



1 Cf. Verworn ('96, 2). » 



