SCIENCE LETTER FROM PARIS. 273 



quantity, before being affected by the quantity of light, that is to say, the power 

 of distinguishing colors. All animated matter, whether animal or vegetable, is 

 sensible to the varied intensity of light. The petioles and leaflets of the sensitive 

 plant become flaccid, when placed in lanterns of violet, blue, or green glass ; 

 they become stiff, when changed to a lantern of yellow or red glass. In the case 

 of those microscopic animals, the daphnia, peculiar to ponds, Paul Bert enclosed 

 a number of them in cracked vase. So long as they were left in the dark, the 

 animals swam about indifferently, but the moment a spectral light passed through 

 the crack, the animalcules rushed to the spot ; now if the light consisted only of a 

 single colored ray, the daphnia crowded in greatest numbers, as the rays are yel- 

 low and red, rather than blue and violet. By what physiological process does 

 the human eye feel not only the quantity, but the quality of light, that is to say, 

 distinguish colors? By the force, more or less strong, with which the ethereal 

 waves shake the sensitive elements of the retina. Such is the cause, altogether 

 mechanical, of the sense of colors. The red and yellow rays, are more percepti- 

 ble than blue or violet, because they possess more energy and strength, when as 

 ether-waves they strike the middle of the retina, leaving a profounder trace. 



Dr. Tholozan, physician to the Shah of Persia, read a paper before the Acad- 

 emy of Science on diphtheria. He stated there is no name either in Persian or 

 Arabic for this disease, and it is not known in Oriental history. It first made 

 its appearance in the centre of Persia, in 1869, spontaneously; it has since at- 

 tacked individuals in different parts of Persia, other than sea-ports, thus proving 

 the malady has not been imported. Its effects are most disastrous in cold weather. 



Paris has a new hospital at Menilmontant, containing 560 beds, each bed 

 having 55 cubic yards of air. The four wings, containing the wards, are wide 

 apart, and five stories high; the fifth story is a spare ward, into which the patients 

 of different wards are conveyed to admit of that vacated being fumigated and 

 cleansed periodically; there are lifts for all the stories, and large fire-places in each 

 ward. Apart from the value of an open chimney as an agent of ventilation, the 

 French surgeons find that a blazing fire produces a most salutary effect on the 

 invalids, especially those capable to sit around it and chat. In addition, the salles 

 are warmed by hot air. The wing devoted to accouchements has a distinct and 

 separated room for each woman, following Dr. Tarnier's plan. The new hospital 

 is the first in Paris, and far superior to that costly failure — the Hotel Dieu. 



Not the least of the wonders connected with the Exhibition, is the building 

 itself; in the 1867 palace, owing to its demi-circumference form, the iron em- 

 ployed could only be afterwards sold as old metal. In the present structure the 

 pieces can be sold without any loss ; indeed the building might be taken down and re- 

 erected in any city in the world. The subsoil of the Exhibition is a marvel ; it 

 consists of a series of double passages — containing 5,000 pillars some ten teethigh 

 — for the purposes of ventilation, gas and water pipes, etc. It is a city of tombs 

 — catacombs under another form. At every twenty yards are ladders, pick axes. 

 etc., so that in case of fire, a guardian has only to raise a trap-door in the floor, 



