aterial enters most
conspicuously;

(a) by the portal veins portal veins and

(b) by the thoracic duct and left superior cava.

Section 49. The following table summarises what we have learnt up to
the present of the physiology of the Rabbit, considered as a
mechanism using up food and oxygen and disengaging energy:--

-Air_ {Nitrogen... returned unchanged.}
{Oxygen... through Pulmonary Vein to--} {see 3.}

-Food_ {Carbo-Hydrates (Starch, Sugar, Cellulose.)} Sugar.
{Protein.} {Peptones.}
{Fat (little in Rabbit.)} {Glycerine, and fatty acids in soups.}
{Rejected matter got rid of in Defaecation.}

1a. {Chyle in Lacteals going via {through} Thoracic Duct and Left
Superior Cava to--} {see 2.}

1b. {Veins of Villi--}
{Portal Vein--}
{Liver--}
{Hepatic Vein and Inferior Cava to--} {see 2.}

2. {Right side of heart; then to lungs, and then to--} {see 3.}

3. {Left side of heart; whence to Systemic Arteries and Capillaries.}

4. {The tissues and -Kataboly_.}

5. {Urea (?Liver) Kidney and Sweat Glands}
{CO2} {Lungs}
{H2O} {Lungs, Kidney, Sweat Glands}
{Other Substances} {Mainly by [Kidney,] Liver and Alimentary Canal}

4. _The Amoeba. Cells, and Tissue_

Section 50. We have thus seen how the nutritive material is taken into
the animal's system and distributed over its body, and incidentally, we
have noted how the resultant products of the creature's activity are
removed. The essence of the whole process, as we have already
stated, is the decomposition and partial oxydation of certain complex
chemical compounds to water, carbon dioxide, a low nitrogenous
body, which finally takes the form of urea, and other substances. We
may now go on to a more detailed study, the microscopic study, or
histology, of the tissues in which metaboly and kataboly occur, but
before we do this it will be convenient to glance for a moment at
another of our animal types-- the Amoeba, the lowest as the rabbit is
the highest, in our series.

Section 51. This is shown in Figure III., Sheet 3, as it would appear
under the low power of the microscope. We have a mass of a clear,
transparent, greyish substance called protoplasm, granular in
places, and with a clearer border; within this is a denser portion called
the nucleus, or endoplast (n.), which, under the microscope, by
transmitted light, appear brighter, and within that a still denser spot,
the nucleolus (ns.) or