2 Livingston : Chemical stimulation of a green alga 



the first section of this problem, and deals with the effects of what 



are termed the positively charged ions from dissociated mineral 



salts. 



In the following pages the term stimulation will be used to 



denote any catalytic effect upon vital activity, brought about by 

 any change of the conditions under which the organism is living. 

 Thus, any substance which, upon entering the protoplasm, causes 

 either an acceleration or a retardation of certain functions, is a 

 stimulating agent Death itself, when it results from poisons at 

 least, is merely the last of a series of stimulation responses, or, 

 rather, it is the final summation of such responses, and appears as 

 a single one only because we have not yet been able to unravel 

 the vast tangle of activities of which it is the resultant. 

 ■ Two ends must be held in view in a research of this kind. 

 First, analysis is to be made of the conditions which bring about 

 the response, and determination of their manner of action. Second, 

 knowing in this way something of the sets of conditions which 

 stimulate, it will eventually be possible, it is hoped, to interpret 

 the latter so. as to. throw light upon the nature of the stimulated 

 processes themselves. It is by this means that we may hope to 

 gain more definite knowledge of the complex system of energy 

 changes which make up vitality. Thus the problem may be 

 approached in somew^hat the same manner as that in which the 

 chemist attacks a new organic compound, by studying in a quanti- 

 tative way the effects of various reagents upon it. In this case of 

 the chemist, the reagents are at least better known than the body 

 to which they are applied, and the same must be true in physio- 

 logical work. For a study of toxic stimulation, a knowledge of 

 reagents comes, of course, from the realm of physics and chemistry. 

 The organism used in the experiments here described is the 

 same form of Stigcoclomttm whose responses to changes in external 

 osmotic pressure were worked out some time ago.* A brief 



* Livingston, B, E. On the nature of the stimulus which causes the change of 

 form in polymorphic green algae. Bot. Gaz. 30 : 289-317. 1900. — Further notes 



norphism in green algae. Bot. Gaz. 32 ; 292-302. 1901. 



The r61e of diffussion and osmotic pressure in plants 132-137, Chicago. 1903. 



(These pages are included in the reprint of the last chapter of the volume, entitled, 



The influence of the osmotic pressure of the surrounding medium upon organisms. 



Chicago. 1903. ) A portion of the resume here given is taken from the last reference. 



poly 



