Page:The Modern Review (July-December 1925).pdf/747

Rh light thrown on the distant screen. The slightest movement of the leaf up or down, can thus be easily magnified some five thousand times.

Here is a plant from which supply of water has been withheld; the leaf is drooping and the indicating spot of light shows a rapid fall. We will now make its pumping mechanism active by making the plant imbibe water containing ether which, in small doses, is a stimulant. Observe how magical the effect is; the down-movement of the spot of light is reversed into a rapid up-movement. I will now stop the plant’s exuberance by poisoning it with a fatal dose of potassium cyanide. Watch the conflict between life and death. The struggle is now ended, and death has at last claimed its mastery. We try in vain to revive the plant and restore the ascent of sap by irrigation with fresh water. Can there be any evidence more conclusive than this in proof of the activity of living cells in propulsion of sap?

My results prove that an identical mechanism maintains the circulation of blood in the animal and propulsion of sap in the plant. A necessary consequence of this is that variations of blood-pressure and sap-pressure should be produced under parallel conditions. The most important factor in causing arterial pressure by the circulating fluid is the pumping activity of the heart. Under stimulating agencies this becomes enhanced with resulting increase of blood-pressure; under depressing conditions the pressure becomes decreased. The radial artery on the wrist is exposed and it is easy to feel the pulse-beat or record it by the Sphygmograph. For demonstration before a large audience, a simple contrivance is shown by which the pulse-beat is magnified by a reflected beam of light. The pulse is beating at the rate of about 72 per minute or say once in a second. The frequency of the beat is not always constant but fluctuates under excitation or depression.

The normal blood-pressure and its induced changes can also be recorded by elaborate contrivances. The record thrown on the screen shows the change in the blood pressure by alternate stimulation and partial inhibition of the activity of the heart-pump. Under normal conditions the up and down-strokes of each constituent pulse are equal. During increasing

blood-pressure, the up-stroke is the larger of the two.

The radial artery on the surface offers an unique advantage in obtaining the record of human pulse. But this method fails when an attempt is made to record the throbbings of an artery in the interior, buried under other tissues.

An attempt to feel the pulse of the plant would, by the very nature of the case, appear to be hopeless. If the plant propelled the sap by periodic pulsations of the active cells, the amount of expansion and contraction of each pulse would be beyond even the highest powers of the microscope to detect. The active cells are moreover buried in the interior of the plant; how could the invisible and hidden be rendered visible?

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Two years ago, I succeeded by means of my Electric Probe, to get access to the smallest unit of life, the ‘life atom’ and record its throbbing pulsation. On making suitable electric connections with a muscle in a state of rest, the galvanometer in circuit remains quiescent. But contraction of the muscle under stimulus causes a sudden deflection of the needle of the galvanometer in a definite direction, the expansive recovery