CONDUCTION WITHIN NERVE CELLS. 607 



sponding to the rhythm at which the nervous impulses have passed 

 along. By both these methods it appears that such nerve cells as 

 those of the motor region of the cerebral cortex, and the motor cells of 

 the anterior horn of the spinal cord, tend, whether stimulated either 

 directly or indirectly (e.g., reflexly), to respond by discharging nervous 

 impulses at the rate of about ten or twelve per second, unless the 

 stimulation be at a less rate than this, in which case the response is at 

 the same rate as the stimulation. Under some circumstances, how- 

 ever, the rate of rhythmic discharge may be more rapid than ten or 

 twelve per second, or it may be as slow as five per second, the muscular 

 response in the latter case being of a clonic character. What it is 

 which determines this difference in different cases and under different 

 conditions, is not at present known ; in discussing the manner in which 

 the nervous impulses pass from one cell to another, we shall have 

 occasion again to refer to it. 



We have so far confined our attention almost entirely to the changes 

 which occur within the limits of a single nerve cell ; we have next to 

 inquire how these changes may be propagated from one nerve cell to 

 another. 



The introduction of the method of Golgi, and especially its employ- 

 ment by Cajal, dealt a severe blow to the then prevalent hypothesis, that 

 the propagation of nervous impulses from cell to cell took place through 

 a continuity of their dendrons, which were thought to be united in a 

 network which everywhere pervaded the grey matter (J. Gerlach). 

 At the same time, it exhibited an explanation by which this hypothesis 

 could be replaced, since it showed that although there may be no 

 continuity of processes of nerve cells, there undoubtedly is close 

 contiguity or even actual contact. This is sometimes effected by 

 the embracing of the body of one cell by the ramifications of the 

 axon of another, 1 sometimes by the interlocking of the dendrons 

 of one cell with the dendrons or with the ramified axon of another, 

 or even of more than one other cell. It is convenient to have a 

 short term by which to speak of the union of one nerve cell with 

 another by this close contiguity of processes with cell body or of 

 processes with processes, presumably without actual continuity of 

 substance. Foster 2 has employed the term " synapse " 3 to de- 

 note such conjunction, an expression which may provisionally be 

 adopted. 



It has been conjectured that the extent of contact of the adjacent nerve 

 cells at the synapses may vary from time to time, such variations being brought 

 about by a contraction or expansion of the ramified processes by which the contact 

 is effected, analogous to the amoeboid movements of protoplasm in general ; and, 

 further, that the effects of drugs in diminishing or increasing the resistance of 

 the nerve centres to the passage of nervous impulses might be produced in 



1 W. A. Turner and W. Hunter {Brain, London, 1899, vol. xxii. p. 123) have described 

 a network covering the cell body of nerve cells in the grey matter of the central nervous 

 system, which they regard as the terminal apparatus of the axis cylinder processes of other 

 nerve cells. A basketdike ending, extending over both cell body and dendrons, was 

 described by Semi Meyer (Ber. d. k. sachs. Gesellsch. d. Wissensch. , malh.-phys. CI., 

 Leipzig, 1897, S. 475), who came to the same conclusion; Martinotti, Ann. di frcniat., 

 Torino, 1897, p. 253; and Golgi, Boll. d. Soc. med.-chir. di Pavia, Milano, April 19, 1898. 

 Cf. also Held, who describes a concrescence of the axon of one nerve cell with the body or 

 dendron of another cell, Arch. f. Anat. u. Entivcklnqsgcsch., Leipzig, 1891, 1893, and 1897. 



2 "Text-book of Physiology," 1897, vol. iii. p. 929. 



3 From aiiv and ainw clasp. 



