TKANSACTIONS OF SECTION D. G07 



of the retina with what is required of it, and finds that the number of objects which 

 he can discriminate in the held of vision is as numerous as, but not more numerous 

 than, the parts of the retina, i.e. the cones wiiich are concerned in discriminatinj^ 

 them. So far he has no dithculty ; but the method of correlation fails him from 

 the moment that he considers that each object point in tlie field of vision is coloured 

 and that he is able to discriminate not merely the number and the relations of all 

 the object points to each other, but the colour of each separately, lie then sees 

 at once that each cone must possess a plurality of endowments for which its 

 structure affords no explanation. In other words, in the minute structure of the 

 human retina, we have a mechanism which would completely explain the picture 

 of which we are conscious, were the objects composino; it colourless, i.e. possessed of 

 one objective quality only, but it leaves us without explanation of the diflerentia- 

 tion of colour. 



lSimilarly,ifwe are called upon to explain the function of a secreting gland, such 

 C.17., as the liver, there is no ditficulfy in understanding that, inasmuch asthe'whole 

 e-land consists of lobules which resemble each other exactly, and each lobule is 

 similarly made up of cells which are all alike, each individual cell must be capable 

 of performing all the functions of the whole organ. IJut when by exact experi- 

 ment we learn that the liver possesses not one function but many — when we know 

 that it is a storehouse for animal starch, that each cell possesses the power of 

 separating waste colouring matter from the blood, and of manufacturing several 

 kinds of crystallisable products, some of which it sends in one direction and others 

 in the opposite, we find again that the correlation method fails us, and that all 

 that our knowledge of the minute structure has done for us is to set before us a 

 question which, though elementary, we are quite unable to answer. 



By multiplying examples of the same kind, we should in each case come to the 

 same issue, namely, plurality of function ivith unity of structure, the unity being 

 represented by a simple structural element— be it retinal cone or cell— possessed of 

 numerous endowments. Whenever this point is arrived at in any investigation, 

 structure must for the moment cease to be our guide, and in general, two 

 courses or alternatives are open to us. One is to fall back on that wom-out Deu^ 

 ex machind, protoplasm, as if it alVorded a sufficient explanation of everythinn- 

 which cannot be explained otherwise, and accordingly to defer the consideration 

 of the functions which have no demonstrable connection with structure as for the 

 present beyond the scope of investigation ; the other is, retaining our hold of the 

 fundamental principle of correlation, to take the problem in reverse, i.e. to use 

 analysis of function as a guide to the ultra-microscopical analysis of structure. 



I need scarcely say that of these two courses the ^/-s^; is wrong, the second ri^ht, 

 for in following it we still hold to the fundamental principle that limig material 

 acts by virtm of its structure, provided that we allow the term structure to be 

 used in a .sense which carries it beyond the limits of anatomical investifation 

 i.e., beyond the knowledge which can be attained either by the scalpel orthe micro^ 

 scope. We thus (as I have said) proceed from function to structure, instead of the 

 other way. 



The departure from the traditions of our science which this change of direc- 

 tion seems to imply is indeed more apparent than real. In tracing the history of 

 some of the greatest advances, we find that the recognition of function has pre- 

 ceded the knowledge of structure. Haller's discovery of irritability was known 

 and bore fruit, long before anything Avas known of the structure of muscle. So 

 also, at a later period, Bichat was led by his recognition of the physiolo"-ical 

 diUerences between what he termed the functions of organic and animal lile to 

 those anatomical researches which were the basis of the modern science of flis- 

 tologv. Again, in much more recent times, the investit.ration of the function of 

 gland celjs, which has been carried on with such remarkable results by Professor 

 Heidenhain in Germany, and with equal success by Mr. Langley in this country 

 has led to the discovery of the structural changes which thev undergo in passing 

 from the state of repose to that of activity ; nor could "l mention a better 

 example than that aflforded (among many others relating to tlie physiology of the 

 nervous system) by Dr. Gaskell's recent and yery important discovery of the 



