652 TF. D. Lang — Bernard'' s Biological Theories of Fossils. 



rather it transcends it by re.^ardiug the cell as one particular kind of 

 grouping of homogeneous units theluselves built on a definite pattern. 

 Thus, while the cell-doctrine lays stress upon the nucleus and the 

 cytoplasm as essential factors of the cell, Bernard emphasizes the 

 nucleus and the linin threads, the cytoplasm being composed of these 

 and a pervading albuminous matrix. The significance of each point 

 of view is seen when cell-aggregates are considered. To the cell- 

 doctrine they are merely aggregates, though, since thej' act as a whole, 

 there is some unknown co-ordinating influence. This, according to 

 Bernard, is exerted by means of the physical continuity of the linin 

 threads from cell to cell, continuous because they have never been 

 separate. For a dividing nucleus implies a division of every 

 chromidial unit of which it is composed and a longitudinal splitting 

 of those linin threads in the plane of division and a lengthening of 

 those at right angles to this plane. 



The invariable presence of linin threads and their continuity from 

 cell to cell is thus the essence of the theorj' from the point of view of 

 the cell-doctrine. And here the critic may find an assailable point. 

 Bernard's position is that, except when chromidia are travelling along 

 them, the linin threads are invisible (with our present powers of 

 vision). The scientific purist may deny the right of assuming the 

 presence of a structure in any case when its existence cannot be 

 proved by definite tests ; the onus of proving the linin threads' 

 existence in every case lies with Bernard. Bernard adduces certain 

 cases wliere the threads are visible, shows that the protoplasm is then 

 in a condition (e.g. when repeated nuclear division is taking place and 

 chromidia streaming along the tiii'eads in consequence, or when waste 

 products are being copiously conveyed along them) when on a priori 

 grounds it is to be expected that the threads will temporarily be 

 visible, and argues that it is fair to assume that they are always 

 present, though often invisible. He thus leaves it for his critics to 

 prove the absence of threads, disarming criticism by presenting 

 a negative for proof. Future work alone will show whether the 

 threads are invariably present. Hitherto thej' have not been sought, 

 and have been noticed only when they could not well be disregarded. 

 It is incumbent upon future workers to have this theory in mind and 

 in its light to test the work already done. It is for this testing that 

 Bernard pleads. 



Bernard's first book, then, miglit be summarized as follows: — 

 Protoplasm, in the simplest manifestation of its structure to which 

 our present powers of vision can take us, consists of a network of linin 

 threads with chromidia at the nodes, bathed in an albuminous matrix ; 

 a particular form of such a network, wherein the chromidia are massed 

 in a ctmtral ball and the linin threads consequently tangled but still 

 radiating from the central mass of chromidia through tlie albuminous 

 matrix to the surface, constitutes the typical cell of the cell-theory. 



II- 



The idea of a cell as a particular grouping of homogeneous units, 

 and at the same time one of many similar units that build up an 

 organism, led Bernard to conceive the possibility of a unit of higher 



