SiGERSON — On Heat as a Factor in Vital Action. 5 



Por:— 



First. By the action of heat we can produce various alterations inform 

 of lifeless matter, similar to those which are seen occurring in liviug 

 matter in the cases quoted. 



Second. In order that such changes should occur in living matter, 

 heat is absolutely necessary. Cold delays and stops them, as in the 

 case of the lifeless matter. A certain quantity of heat is needed. Too 

 much as well as too little heat causes cessation of movement; there is 

 a maximum as there is a minimum limit. 



We come now to another class of movements which have likewise 

 been termed vital. I refer to circulatory movements, such for instance 

 as intra-cellular rotation, and cyclosis. In a given cell, we may occa- 

 sionally observe its fluid contents in motion, made visible by a number 

 of little granules that are carried along with it. This movement may 

 be simple rotation, or it may take place in a spiral direction ; though 

 different courses may be taken in adjoining cells, the movement usually 

 keeps on, in one direction in the same cell. Various ingenious theories 

 have been devised to account for this. 



If, now, we take a drop of oil and approach it to the flame of a candle, 

 it can be seen that the oil, first at rest, is set in motion, slow or quick 

 in accordance with the less or greater degree of heat exhibited. A 

 little dust shaken into it allows the rotation of the granule-bearing 

 currents to be easily observed by those who have a keen vision for mi- 

 nute objects. A slender baton of wax may be used : approaching the 

 flame, the point melts, a drop forms, and then rotation is set up. If 

 instead of having a rounded di'op, we confine a fluid in a glass vessel 

 shaped like a long cell, the fluid inside, by approximation to the flame, 

 can be caused to move longitudinally. In a free fluid the particles are 

 caused by heat to describe an ellipse — they seem to return in their 

 courses, and this appears to 'be the case where heat impinges on the 

 surface, so that we might expect to find a kind of circulation or ro- 

 tation set up in water under the infl uence of the sun, apparently similar 

 in kind to the motion of the celestial bodies. 



To return to rotation in cells : — 



First. Heat is capable of causing rotation in fluids. 



Second. The rotation observed in cells absolutely requires heat. It 

 chilled, the motion is slackened ; if set under a certain degree of cold, 

 it is stopped altogether. 



Movement displaying different phenomena is that which has been 

 termed cyclosis. This is shown in a plexus of latex-bearing vessels; 

 it has been described as analogous to the capillary circulation in animals. 

 There is no organ to make a vis a tergo, and yet there is movement 

 through vessels in which there is no contraction ; neither can it be 

 attributed to a vis a fronte. It seems to take place in all directions, 

 and has been considered a peculiar vital movement connected with 

 formative functions. 



If now we bring a heated body over the surface of a fluid, we will 

 find that currents will be formed in all directions. In one case, under a 



