216  Natural-Historical Collections. 
fera, and that the proportion of genera and species has only arrived by degrees or 
by successive stages, at a state resembling that which we now behold,—it was 
natural to inquire if the vegetable kingdom had. not undergone analogous alter- 
ations ; but it was no easy matter to answer such a question, because it would be 
requisite for that purpose to determine with precision the species of fossil vegeta~ 
bles ; andthe principles of this determination, in the ordinary methods, are founded 
upon the observation of such delicate organs, that we can never hope to recognize 
them in these impressions, or preserved remains of the vegetation of the former 
world. 
M. Adolphe Brongniart, who has pursued this problem with an aduicabile 
perseverance, has, therefore, found it necessary to invent a particular method, and 
to discover recognizable characters in the most constant and marked appearances, 
presented by the surface and structure of the stems, by the distribution of the 
nerves of the leaves, and by other particularities of organization. Applying this 
method to the objects with which the strata of the globe have furnished him, he 
has commenced to publish a work wherein he is to classify and describe upwards 
of 500 species of fossil vegetables, and to make known all the circumstances of 
their positions. He has presented to the Academy an abstract of his researches, 
in which he establishes the fact, that in a certain number of successive forma- 
tions, vegetables belonging to the same genera and the same families, are often 
found with little variation, and that even the numerical relations of the great 
classes remain nearly constant, whilst in other series of formations, a portion of 
the genera and families change suddenly, and the relations of the classes become 
very different. The points where he has observed these rapid changes, have 
furnished his geological vegetable epochs, if one may so express it, and he has 
thus fixed fourperiods, during each of which the vegetation has only presented 
variations of little moment, but the passage of which from one to the other has 
been marked by important charges. 
Anaiomy and Animal Physiology._M. Magendie has collected together. his 
observations upon the brain and the fluid which moistens it, as well as the spi- 
ual marrow, on which we have already reported in our preceeding analysis ; and 
he pr résenitet them at the public meeting of the last year. 
An adult man has about three ounces of this liquid; women have more; in 
aged men, in whom the mass of the brain is diminished, the fluid is increased to 
about 6 or 7 ounces. -It forms a film of one or two lines around the brain, and 
in certain circumstances, and certain. places, of nearly an inchs; which, by the 
way, appears to M. Magendie a very strong objection against a system which is 
based on the intimate relations between the form of the cranium, and that of the 
brain. 
Much is wanting that the dimensions of the brain should be as uniform as 
one would be led to believe, in judging from the fixed form of the cranium. In 
all disorders of a certain duration, in which the body is much wasted, the brain 
undergoes a similar diminution ; it regains, with the progress of convalescence, . 
its former bulk, and one of the principal offices of the fluid in question, is to 
supply during these conditions the void which is produced. The most ferocious 
animal, from which it has been removed by tapping, becomes calm and motion- 
less ; put its natural state returns after a very short interval, during which the 
fuid is regenerated. If it be restored after being made cold, the animal puts on 
2 general tremor. If water heated to the same temprature be substituted for it, 
the animal falls into an extreme agitation, and appears to have lost its instinct 
and its faculties. 
M. Magendie has investigated the condition of this fluid during mental dise 
eases. Individuals who have become idiotic and old men in their dotage, afforded 
it in large quantity, often as muchas 6 or 7 ounces ; in them it occupied the sur- 
tace of the brain, distended the cavities, and displaced all the parts. It also con- 
siderably fills and distends the ventricles in madness, whatever may be the kind ; 
but then it does not accumulate on the surface of the brain. In individuals pos- 
