DR. H. WATNEY ON THE MINUTE ANATOMY OF THE THYMUS. 
1077 
Staining by means of extract of Brazil 'wood. 
This extract is treated with alum, in the same manner as that from hsematoxylin 
woods. The colour is very beautiful, and varies from dull red to carmine, according 
to the character of the alum used in making the solution. The extract stains in much 
the same manner as hsematoxylin, and can be used with it as a double staining. There 
are three kinds of wood in the English market called Brazil wood, i.e., Lima chips, 
Sappan wood, and Brazil wood. They all contain a staining substance : Brasilin, which 
changes from yellow to red, as hsematoxylin changes from yellow to bluest 
General Observations. 
The thymus was examined in the human foetus and the Child, and in the following 
animals : the Hedgehog, the Cat, the Hog, the Lamb, the Calf, the Ox, the Alpine- 
Marmot, the Bat, the Guinea Pig, the Babbit, the Pelican, the Turkey, the Pigeon, 
the Chick, the Alligator, the Snake, the Tortoise, the Frog, the Axolotl, the Cod-fish, 
and the Bay-fish. 
The thymus first appears in early embryonic life. It increases rapidly in size during 
the life of the embryo, and during the early part of the growth of the animal. The 
time at which it ceases to enlarge, and the duration of its involution, differ considerably 
in the different classes of Vertebrates, and in the different species. In Mammals it 
decreases slowly, does not get much smaller until adult life, and does not finally dis¬ 
appear until some period of adult life has passed.| In Birds it has in most instances 
disappeared before adult life, and the same is true of the thymus of the Frog. In the 
Tortoise and the Bay-fish the thymus is v6ry large in large specimens, as in a Bay 
three feet five inches wide; however, in the large Bays the thymus has been in a 
great measure transformed into connective tissue. 
The involution has been traced in the Ox, Cat, Dog, Guinea Pig,§ Bird, Tortoise, 
and Bay-fish. 
The position of the thymus varies much in different animals, and has been carefully 
described by Simon (2), Leydig (55), Aeanassiew (33), and others ; so that there is no 
need to say any more, than that in Mammals it is found either in the thorax on the 
pericardium, as in the Dog; or in the neck, as in the Guinea Pig where the follicles 
are contiguous to the salivary gland ; or extending from the pericardium to the thyoid, 
as in the Child ; or even nearly to the angle of the jaw, as in the Calf. In Birds, it 
* See Fluckiger and Hanbury ‘ Pharmacographia,’ p. 216, 2nd edit., 1879. 
f I have to thank Messrs. Hearon and Squire, and Messrs. Lescher and Evans, ior taking considerable 
trouble to procure me the various hsematoxylin and Brazil woods. 
J It is in consequence of the want of this knowledge that it has been described by many observers as 
being permanent. I have seen a thymus in a man fifty years old. 
§ There is some difficulty in obtaining old Guinea Pigs, as it is difficult to ascertain the ages of the 
animals; and the breeders usually have no knowledge of the age of any given animal. 
