EFFECT OF ELECTKICAL AND OTHER STIMULE UPON PilOTOPLASM. 177 



Many reagents in solution influence the activity of protoplasm. Some of these 

 act by adding to or subtracting from the water which it contains. As a general 

 rule the imbibition of water up to a certain point, varying according to the 

 source of the protoplasm which is under observation (Thoma), accelerates the 

 activity of the protoplasm, but beyond that point addition of water produces a 

 destructive effect. A comparatively slight amount of desiccation is, so far at least 

 as regards the protoplasm of the higher animals, destructive of vitality, but this 

 statement does not hold good for the protoplasm of many of the lower animal 

 and plant organisms. 



Amongst reagents acids, although very weak (even carbonic acid), stop the 

 contractile manifestations ; alkalies, on the other hand, if sufficiently dilute, increase 

 at first their activity. They are stopped by chloroform and ether, but may be 

 again resumed on the removal of those vapours. Some poisons (e.g., veratria) 

 rapidly arrest the movements of cells. 



Effect of electrical and other stimuli upon protoplasm. The effect of 

 electrical stimulation upon protoplasm which is exhibiting either amoeboid or 

 streaming movement is, if sufficiently strong, to cause an immediate cessation of 

 those movements, accompanied by a withdrawal into the main substance of any 

 processes that may have been protruded. If the stimulation cease the movements 

 will recommence, provided the shock has not been so severe as to injure the living 

 substance. 



Abrupt changes of temperature, and mechanical stimulation, such as is pro- 

 duced by sudden pressure or harsh contact, act in a similar manner. 



Further considerations regarding the structure of protoplasm. If the 

 pseudopodia of a white blood-corpuscle are observed with a high power of the micro- 

 Fig. 205. AN AMCEBOID PALE CORPUSCLE OP THE NEWT, 



KILLED BY INSTANTANEOUS APPLICATION OF STEAM, 



SHOWING THE STRUCTURELESS APPEARANCE OF THE 



PSEUDOPODIA. (Drawn by D. Grunn. ) 



scope, they appear when first thrown out 

 from the body of the corpuscle to be per- 

 fectly clear and homogeneous as if com- 

 posed of hyaloplasm alone. Subsequently 

 the reticular part of the protoplasm may 

 flow into the pseudopodium. This struc- 

 tureless character of the pseudopodia can 

 be well observed if a preparation of the 

 blood of the newt be made and set aside for half-an-hour or more until the white 

 blood corpuscles have had time to throw out broad flattened pseudopodia which 

 spread themselves over the under-surface of the cover-glass. If now a jet of steam 

 be allowed to play for a moment upon the cover-glass, these corpuscles are instantly 

 killed without having been able to withdraw the pseudopodia. They can then be 

 hardened and stained, and observed with the highest powers of the microscope, 

 when it is found that the thin extended portions of protoplasm show no trace of 

 structure but appear completely homogeneous, in decided contrast with the main 

 part of the cell, which exhibits distinctly the spongio-plasmic network. 



Strieker has lately published a photograph of the white blood-corpuscle of a 

 Proteus anguineus, which demonstrates the same fact. In this photograph, which 

 was taken from the living amoeboid cell by an instantaneous method, the body of 

 the cell, which is nearly spherical, is beautifully reticular, whilst a thin external 

 layer and a pseudopodium, which is being protruded, appear completely 

 homogeneous. 



