n 
tHE PRINCIPLES OF BIOLOGY. 
of tlie latter as exhibited in the action of diastase in germi¬ 
nation, of yeast in fermentation, of the vinegar plant 
in acetification, and of the production of prussic acid by 
the action of synaptase on amygdalin. In conclusion, 
attention may be drawn to the vast difference between 
plants and animals in the amounts of nitrogen they 
contain, proving that, if the functions of the former are not 
to cease, light is absolutely indispensable, while for the 
growth of the latter it is not requisite. Fungi appear to be 
an exception to this rule, as light is positively inimical to 
their growth, and they are known to thrive best when nearly 
or quite excluded from its influence. It is generally recog¬ 
nised, however, that these vegetable forms contain much 
nitrogen, and in this respect resemble animals. 
It is also worthy of remark that although those portions 
of plants which possess least nitrogen need sunlight, those 
which have most nitrogen, viz., the seeds, develop and will 
germinate in the dark. Thus while the ferments previously 
alluded to are all nitrogenous, their very activity seeming to 
be due to nitrogen, those parts of living animals which 
possess the greatest vital activity contain also, comparatively 
speaking, the largest amount of this element. The meta¬ 
morphosis of a substance, such as sugar, in the body and out 
of the body may be contrasted; it will then be proved that 
while in the living organism sugar is rapidly changed into 
carbonic acid and water, out of the body it has to go through 
several chemical conversions admitting of experimental 
demonstration, before these results are attained, it being first 
changed by fermentation into alcohol and carbonic acid, then 
into acetic acid, and lastly by further oxidation into carbonic 
acid and water. As, therefore, these changes in the body are 
clearly not produced by chemical and thermal actions solely, 
it may be inferred that they are brought about by means of 
that indirect influence known as catalysis. 
Remedy for Damp. —When a solution of bichromate of potash 
(the crystals dissolve readily in hot water) is applied to any surface 
exposed to sunlight, and allowed to dry, it forms a coating which is 
very impervious to moisture. As the application of two coats of 
the solution (mixed with size to make it adhere) the walls of damp 
rooms, cellars, &c., may be made quite dry. The action of light pro¬ 
duces a chemical change in the bichromate, which gives it this valuable 
property. Bills that have been posted on walls, &c., by means of size 
containing a little bichromate of potash (Jib. to each gallon of size), 
adhere so firmly that it is impossible to remove them by any process 
short of scraping away the surface of the wall. 
