Duration of Variations

Variations in blood-supply fall into one of twoclasses :

1. temporary deviations from the norm, caused by conditions immediately preceding the variation in blood-supply;
2. and more permanent deviations caused by some pathological defect .

The temporary deviations can be corrected by appropriate exercise ; the pathological condition^[1] needs medical attention. One very interesting example has come to my notice. It was a rather pronounced case of Renaud's Disease^[2]. Circulation, as soon as the weather became reasonably cold, stopped at the metacarpo-phalangeal joints leaving all the fingers bloodless. The greenish-white pallor of the fingers contrasted sharply with the normal colouring of the body of the hand. Naturally all sensitivity of the fingers was lost; a deep pin-prick would cause neither pain nor a sign of blood. Piano-playing was impossible because the finer finger-movements could not be executed. The fact that it was impossible to know when the finger touched the key did not disturb as much as might be supposed. This is because our kinesthetic sense depends much more on sensations of strain and muscular position than upon pure cutaneous^[3]sensations. In the case cited vigorous rubbing of the hands re-estab lished circulation sufficient ly, but not unt il a material part of the lesson-time had been consumed.

Variations in blood supply may affect either the quality or the quantity of blood and lymph.^[4] They are caused by the condition of the blood itsclf; the condition of the heart, arteries, capillaries, and veins; distribution of the blood vessels ; posture of the body; exercise ; general bodily condition.
The condition of the blood, its percentage of leukocytes^[5] phagocytes, platelets, and lymph^[6] determines, among other things, its specific gravity and fluidity, its clotting coefficient and chemical value in nourishing the tissues and removing waste-matter from them.
The condition of the heart, its readiness to respond to variations in the intensity of demands made upon it and the contractility of its muscles, together with the functioning of its valves, determines the amount of blood sent to any part of the body within a given time and hence the nourishing value of the circulation. The condition of the blood-vessels, the permeability of the capillary walls, the contractility of the arterial and venal walls as well as their pliability determines the amount of nutrition reaching the tissues and the rate of blood-flow. A rich network of capillaries ensures an even distribution of blood for all parts of the body thus supplied. This, in turn, results in added nutrition and improved response of nerves and muscles.

[1]pathological condition:A pathological condition refers to an abnormal state of an organism, characterized by dysfunction at the anatomical, physiological, or biochemical level. This dysfunction can manifest as various signs and symptoms depending on the specific condition.

[2]Renaud's Disease: Raynaud's disease is a condition that affects the blood vessels, specifically the smaller arteries, in the fingers and toes. It causes these blood vessels to narrow in response to cold temperatures or stress, which leads to a decrease in blood flow.

[3]cutaneous: Cutaneous means of, relating to, or affecting the skin. It is a technical term used in medicine, biology, and other fields to describe anything associated with the skin.

[4]lymph : n. [L. lympha, spring water, altered (after unrelated Gr. nymphe: see NYMPH) < OL. limpa, lumpa]
2. a clear, yellowish fluid resembling blood plasmas, formed in intercellular spaces and in the lymphatic vessels of vertebrates 3. the clear liquid given off from inflamed body tissues.

[5]eukocyte n.: [see LEVCO -& - CYTE] any of the small, colorless cells in the bloody, lymph, and tissues which are important in the body's defense against infection; white blood corpuscle- leukocytic adj.