572 EEPORT— 1882. 



corresponding increase in tiie lymph produced. Again, when llie chorda tympani 

 is stiumlated in an animal into whose blood atropia has been introduced, the ^'as- 

 cidar dilatation which is produced, and which is tlien unaccompanied by secretion, 

 does not lead to an increased production of lymph, which would make itself evident 

 by the gland becoming (Edematous. How then are we to account for the flow of 

 water through a gland ? By ascribing it to an influence which is exerted by the 

 gland-cell, in the iirst place, upon the liquid which environs it, viz. the lympli. 

 And accordingly, even in the case of the glomendi of the kidney, we conclude that 

 the water is separated as a direct result of the activity of the layer of trans- 

 jjarent epithelium cells which cover them. Ilering has advanced a strictly physical 

 theory, which would account for the mode in which certain cells exert this in- 

 fluence, by supposing that there is produced within them bodies which, like mucin, 

 have a great affinity for water and which then pass into the secretion ; and which 

 therefore lead to a current of water passing through the cell ; but the theory is one 

 Avhicli cannot be admitted, because, as Ileidenhain points out, the passage of water 

 througli a gland occurs iu cases where there is no constituent in the cells at all 

 resembling mucin in its affinities or behaviour towards water. 



I feel inclined to say that the specidations, necessarily indefinite though they 

 are, of Professor Ileidenhain aftbrd the best explanation of the phenomena. Heiden- 

 liain starts from the fundamental fact that during secretion only as much water 

 passes out of the blood-vessels of the gland as appears in its secretion, seeing that, 

 however long the process of secretion may continues, the gland never becomes 

 oedematous, nor does the current of lymph from it increase. 



The volume of liquid fllteied through the blood-capiUaries adjusts itself 

 exactly to the volume of liquiil separated by the cells. This equality in the 

 .amount of liquid secreted and filtered appears oidy explicable on the supposition 

 that the act of secretion is the cause of the current of water — in other words, that 

 the water wliich the cells lose in the formation of the secretion generates changes 

 in them which can only be compensated for by an abstraction of water from the 

 immediate enviromnent. 



Within certain limits, Ileidenhain continues, we may form purely jihysical 

 conceptions of the process. AVe may conceive, for instance, the whole protoplasm 

 of the cell to have a certain affinity for water. The cells at their contact with the 

 basement membrane may be supposed tti be able to abstract water from it ; the 

 loss which the membrane sustains will be made up by the lymph, and this again 

 will influence the blood in the capillaries. 



The passage of water into the cells will go on until a period of equilibrium is 

 attained ; but at that time the current of water from the capillaries through the 

 lymph to the cells will cease. We may conceive further, reasons Ileidenhain, 

 tliat the passage of water out of the cell is hindered Ijy such obstacles to the pro- 

 cess of filtration as are represented by resistance opposed to it by the superficial 

 border layer of protoplasm. If we now conceive that — for example, as a result of 

 nerve-stimidation — the gland-cells pour out water, the condition of equilibrium 

 which existed between cell, basement membrane, lymph, and capillary will be 

 disturbed, and a current of liquid set in from the last to the first, and continue as 

 long as the activity of the cells continues. 



It is not difficult moreover, Ileidenhain remarks, to form physical conceptions of 

 the processes whereby water may be separated from the cell itself. It is conceiA'- 

 able, for instance, that the protoplasm of the cell may contract after the manner 

 which occurs in many infusoria, and which in them leads to the accumulation of 

 water in droplets, forming vacuoles, except that in the case of the secreting cells 

 the water is poured out on the outside and not on the inside of the cells. Or, 

 again, it is possible that on the gland-cell passing into the condition of activity an 

 increased production of GOo may occur, leading to an increased diflusion of water 

 outwards. 



So far, I have quoted Professor Ileidenhain, for the most part in his own 

 words. Let me add, however, that the two hypotheses which he advances as 

 possible explanations of the mechanism of secretion of water by the cell rest upon 

 the most probable grounds, as upon the presence of the intra-cellular protoplasmic 



