82 PHYSIOLOGY OF THE DOMESTIC . ANIMALS. 



GENERAL CONDITIONS GOVERNING PROTOPLASMIC MOVEMENT. 

 The motions of protoplasm are governed by a large number of con- 

 ditions which are similar for protoplasm, whether of animal or vegetable 

 origin. This fact therefore points to the identity of protoplasm of ani- 

 mal and vegetable forms of life. 



1. Temperature.— For every variety of protoplasm there is an 

 upper and lower temperature beyond which spontaneous motion ceases. 

 The minimum temperature at which motion is possible is usually 0° C; 

 the maximum is 40° C. Between these limits the rapidity of motion 

 usually increases with the increase of temperature, and the temperature 

 at which the motions are most active usually lies several degrees below 

 the maximum temperature, at which point heat-tetanus, or heat-rigor,— 

 in other words, universal contraction of protoplasm,— occurs, resulting 

 in the assumption of spherical forms analogous to the condition pro- 

 duced by prolonged mechanical, chemical, or electrical irritation. If the 

 temperature is then reduced, the protoplasm may regain its power of 

 spontaneous contractility. At the maximum temperature no optical 

 changes occur in the protoplasm, but if the temperature is raised above 

 this point the protoplasm becomes shriveled and opaque from the coagu- 

 lation of the albuminoids of protoplasm. Vacuoles often form, and the 

 power of contractility is permanently lost. As the temperature is 

 reduced toward the minimum the movements become slower, and con- 

 tractility is Anally extinguished. No optical changes are, however, so 

 produced, and an increase of temperature will now renew the power of 

 contractility. Contractility is therefore destroyed by an excess of heat, — 

 is suspended by a low temperature. 



The changes in shape, as a consequence of change in temperature, are 

 represented in Fig. 53. From a to c the temperature was 12° C. The 

 protoplasm — the white blood-corpuscles of the frog — during that time 

 changed its form but little. The preparation was then placed on the 

 warm stage of the microscope and heated to 50° C. Almost imme- 

 diately the movements became more active, passing through the forms as 

 shown from d to I. At m commencing and at n complete heat-rigor is 

 shown, while at o and p are shown the commencing movements restored 

 by subsequent cooling. 



2. The Degree of Imbibition. — The amount of water held in com- 

 position by the protoplasm is also of influence on the capability for 

 spontaneous motion. For every form of protoplasm there is a maximum 

 and minimum quantity of water of imbibition beyond which movement 

 ceases. Contraction is impossible when, as a rule, less' than 60 per 

 cent, or more than 90 per cent, of water is held by protoplasm. 

 Within these limits the rapidity of contraction increases with the amount 



