12 



KNOWLEDGE. 



January, 1913. 



any part of the protoplast may be, according to the 

 needs of the cell, transformed by chemical processes 

 into any other, and the most striking instances in 

 support of this hypothesis are, perhaps, to be seen in 

 the origin of the plastids from 

 the cytoplasm, and in the 

 formation of zymogen gran- 

 ules from the living substance 

 of the cell. Although this 

 conception is open to consider- 

 able criticism, it is one which 

 has to be taken into account ; 

 for it is well known that the 

 protoplast, both animal and 

 vegetable, is capable of a 

 certain degree of adaptation 

 to changed conditions of exist- 

 ence, and that structural 

 variations in the cell are by no 

 means uncommon under these 

 changed conditions. The 



hypothesis, then, seems to be 

 provisionally a sound one, but 

 requires more discussion before 

 it can be placed in the category of the more definite 

 biological conceptions of the cell ; more than this 

 cannot be said at present, owing to lack of evidence. 



Certain Problems Con- 

 nected with Cell- 

 Metabolism : The 

 Probable Causes of 

 Perverted Metabol- 

 ism: Reaction of 

 the Protoplast to 

 Poisonous Substan- 

 ces and the Various 

 Types of Irritant. 



Some of the most interest- 

 ing cell-problems are those 

 relating to the unorganised 

 ferments or enzymes manufac- 

 tured by the cytoplasm, and 

 the question of certain sub- 

 stances which are produced 

 in the cell consequent upon 

 irritation by the presence of 

 bacteria or morbid influences 

 in the immediate vicinity of 

 the cell. The enzymes ap- 

 pear to be protein-like bodies 

 which have a remarkable 

 action upon (a) Carbohy- 

 drates, (b) Proteids, (c) Fats 

 and (d) Glucosides, existing 

 in the cell ; the main factors 

 in their action upon these 

 bodies seem to consist in a 

 process whereby water is first 

 of all synthesised with them to form a somewhat 

 unstable compound, and subsequently this com- 

 pound is broken up again, with the result that 

 several simple substances are formed, some of 



Figure 18. 



A Photo-micrograph of the definitive nucleus 

 in the embryo-sac of an Angiosperm {Helle- 

 borus niger) to show the nuclear membrane, 

 chromatin, reticulum and one large nucleolus 

 (to the left is the nucleus of the egg-cell). 



(including also the 



Figure 19. 

 A Photo-micrograph of a single cell of the Endo- 

 sperm in the embryo-sac of an Angiosperm to show 

 (on the left side) bridles of cytoplasm passing 

 through the cell-wall to an adjacent protoplast. 

 Note the oval nucleus with several nucleoli. 



which are capable of being directly utilised during 

 cell-metabolism for constructive purposes. The 

 manner in which the enzymes are produced from 

 the zymogen-granules is not as yet fully understood; 

 it appears that the zymogen 

 may be converted into the 

 enzyme in certain cases by the 

 action upon the former of a 

 dilute acid or alkali, and that 

 the production of zymogen 

 in the cytoplasm is of a con- 

 structive (anabolic) nature, 

 whereas the conversion of 

 zymogen into ferment belongs 

 to the destructive (katabolic) 

 type of reaction. 



Again, it is now well-estab- 

 lished that in the case of the 

 so-called organised ferments 

 (Saccharomyces, B. hutyricus, 

 B. lactis and so on) the actual 

 enzyme is a product manu- 

 factured in the actual yeast 

 cells and bacilli, and then 

 passed out of the cells into the surrounding 

 medium ; many of the toxins and toxic proteids 

 so-called toxalbumoses are of 

 this nature, otherwise known 

 as intracellular toxins ; but in 

 certain cases, as, for instance, 

 when bacteria gain entry into 

 the tissues of the animal bod} - , 

 the actual cells of the tissue 

 may react in a special manner 

 and produce anti-toxins which 

 tend to limit the production 

 of toxins by the bacteria, or 

 else neutralise such toxins. 



Of late years two other 

 types of enzyme have been 

 shown to exist in the cell in 

 some cases ; these are the 

 oxidising and reducing en- 

 zymes (oxidases and reduct- 

 ases) and they have been found 

 to be present in many plant 

 cells. The oxidases are 

 capable of furthering the 

 oxidation of the cytoplasm in 

 the absence of free oxvgen, 

 and it appears that the instan- 

 ces of so-called anaerobic 

 respiration (certain bacteria) 

 are due to the presence of 

 some form of oxidase. 



The question of proteid- 

 metabolism in the cell is a 

 problem which still remains 

 largely unsolved ; it seems, 

 however, to be established that one of the inter- 

 mediate stages consists in the combination of 

 three classes of bodies, viz., the amido-acids, some 

 form of carbohydrate, and a sulphur-compound; but 



