MOVEMENTS OF IRRITATION. 419 



a glass rod a few drops of not too concentrated alcoholic fuchsin 

 or methyl violet solution. The drops do not spread themselves at 

 their edges uniformly over the glass, but there form, now at one 

 point and now at another, protrusions of the fluid, and we involun- 

 tarily recall amoeboid protoplasmic movements We pour distilled 

 water into a carefully cleaned glass dish, and drop small frag- 

 ments of camphor on to it. The particles of camphor, as they 

 very gradually dissolve in the water, fall into very active move- 

 ment, which I have often seen to continue for hours. 



If by means of a glass rod, we bring a trace of olive oil on to 

 the water on which the camphor is moving, the movement rapidly 

 ceases. The spreading oil, viz., raises very considerably the 

 surface tension of the water, and hence the phenomenon described. 

 If a drop of cod-liver oil is treated with 0*25 p.c. soda solution, 

 very interesting phenomena of spreading appear. There are 

 changes in the surface tension which appear quite sufficient to 

 account for the movements in question, and changes in tension 

 also without doubt play a great part in connection with protoplas- 

 mic movements. Yery thorough study is still required, however, 

 in order to comprehend in detail the complicated phenomena as 

 they are exhibited in the living cells. 3 



Temperature has a very important influence on the rate of 

 movement of the protoplasm. At a low temperature the proto- 

 plasm moves slowly. With rising temperature the rate of 

 movement increases, until the optimum temperature is passed 

 (the optimum temperature for protoplasmic movement in the 

 leaf-cells of Elodea, for example, lies, according to -Velten, 4 at 

 36 C.), when it again diminishes. It is instructive to determine 

 by observation that at a particular temperature, not far removed 

 from that at which the cells are killed, the protoplasm passes into 

 a state of transient heat-rigor. 



We warm some water in a porcelain dish on the water-bath. 

 Into the water dips a thermometer. We now remove a strip of 

 epidermis from a young part, say a young leaf-stalk, of a plant of 

 Cucurbita Pepo, observe the occurrence of circulation in the pro- 

 toplasm of the hair-cells, note carefully some of the hairs, and 

 then with the forceps immerse the strip of epidermis in the heated 

 water close to the bulb of the thermometer. If the epidermis is 

 left for two minutes in water at a temperature of 46 C., it will 

 be seen on examination under the microscope that all movement 

 of the protoplasm in the hair-cells has ceased. The protoplasm 



