|
Main
- books.jibble.org
My Books
- IRC Hacks
Misc. Articles
- Meaning of Jibble
- M4 Su Doku
- Computer Scrapbooking
- Setting up Java
- Bootable Java
- Cookies in Java
- Dynamic Graphs
- Social Shakespeare
External Links
- Paul Mutton
- Jibble Photo Gallery
- Jibble Forums
- Google Landmarks
- Jibble Shop
- Free Books
- Intershot Ltd
|
books.jibble.org
Previous Page
| Next Page
Page 47
The infectious diseases are pre�minently the diseases of the first
third of life. After the age of forty man represents a select
material. He has acquired immunity to many infections by having
experienced them. Habits of life have become fixed and there is a
general adjustment to environment. The only infectious disease which
shows no abatement in its incidence is pneumonia, and the mortality in
this increases with age. Between thirty-five and fifty-five man stands
on a tolerably firm foundation regarding health; after this the age
atrophies begin, the effects of previous damage begin to be apparent,
and the tumor incidence increases.
FOOTNOTE:
[1] This was the case of a woman, by occupation a cook, whose numerous
exchanges of service were accompanied by the appearance of cases of
typhoid fever in the families. This became so marked that an
examination was made and she was found to be a typhoid carrier and as
such constantly discharging typhoid bacilli. She is now isolated.
CHAPTER X
INHERITANCE AS A FACTOR IN DISEASE.--THE PROCESS OF CELL
MULTIPLICATION.--THE SEXUAL CELLS DIFFER FROM THE OTHER CELLS OF THE
BODY.--INFECTION OF THE OVUM.--INTRA-UTERINE INFECTION.--THE PLACENTA
AS A BARRIER TO INFECTION.--VARIATIONS AND MUTATIONS.--THE INHERITANCE
OF SUSCEPTIBILITY TO DISEASE.--THE INFLUENCE OF ALCOHOLISM IN THE
PARENTS ON THE DESCENDANTS.--THE HEREDITY OF NERVOUS
DISEASES.--TRANSMISSION OF DISEASE BY THE FEMALE ONLY.--HEMOPHILIA.--
THE INHERITANCE OF MALFORMATIONS.--THE CAUSES OF
MALFORMATIONS.--MATERNAL IMPRESSIONS HAVE NO INFLUENCE.--EUGENICS.
The question of inheritance of disease is closely associated with the
study of infection, and the general subject of heredity in its bearing
on disease can be considered here. By heredity is understood the
transference of similar characteristics from one generation of
organisms to another. The formation of the sexual cells is a much more
complex process than that of the formation of single differentiated
cells, for the properties of all the cells of the body are represented
in the sexual cells, to the union of which the heredity transmission
of the qualities of the parents is due. In the nucleus of all the
cells in the body there is a material called _chromatin_, which
in the process of cell division forms a convoluted thread; this
afterwards divides into a number of loops called _chromosomes_,
the number of which are constant for each animal species. In cell
division these loops divide longitudinally, one-half of each going to
the two new cells which result from the division; each new cell has
one-half of all the chromatin contained in the old and also one-half
of the cytoplasm or the cell material outside of the nucleus. The
process of sexual fertilization consists in the union of the male and
female sex cells and an equal blending of the chromatin contained in
each (Fig. 22). In the process of formation of the sexual cells a
diminution of the number of chromosomes contained in them takes place,
but this is preceded by such an intimate intermingling of the
chromatin that the sexual cells contain part of all the chromosomes of
the undifferentiated cells from which they were formed. The new cell
which is formed by the union of the male and female sexual cells and
which constitutes a new organism, contains the number of chromosomes
characteristic of the species and parts of all the chromatin of the
undifferentiated cells of male and female ancestors. As a result of
this the most complicated mechanism in nature, it is evident that in a
strict sense there can be no heredity of a disease because heredity in
the mammal is solely a matter of the chromosomes and these could not
convey a parasite. The new organism can, however, quickly become
diseased and, by the transference of disease to it and by either
parent, there is the appearance of hereditary transmission of disease,
though in reality it is not such. The ovum itself can become the site
of infection; this, which was first discovered by Pasteur in the eggs
of silkworms, takes place not infrequently in the infection of insects
with protozoa. In Texas fever the ticks which transmit the disease,
after filling with the infected blood, drop off and lay eggs which
contain the parasites, and the disease is propagated by the young
ticks in whom the parasites have multiplied. The same thing is true in
regard to the African relapsing or tick fever, which is also
transferred by a tick. In the white diarrhoea of chickens the eggs
become infected before they are laid and the young chick is infected
before it emerges from the shell. It is highly improbable, and there
is no certain evidence for it, that the extremely small amount of
material contributed by the male can become infected and bring
infection to the new organism. In the cases in which disease of the
male parent is transferred to the offspring, it is either by an
infection of the female by the male, with transference of the
infection from her to the developing organism, or with the male sexual
cells there may be a transference to the female of the infectious
material and the new organism may be directly infected. No other
disease in man is so easily and directly transferred from either
parent to offspring as is syphilis, and the disease is extremely
malignant for the foetus, usually causing death before the normal
period of intra-uterine development is reached.
Previous Page
| Next Page
|
|