Masterpieces from the Louvre: The Collection of Louis la Caze, The Wallace Collection, London

It's that time of year again: florists wrap long-stemmed roses in their sleep, chocolatiers whip up industrial quantities of ganache, and singletons mumble to themselves about the crassness of it all. Fortunately, you don't have to have a significant other to appreciate Masterpieces from the Louvre, a small part of the huge collection bequeathed to the museum by Louis La Caze in 1869. You should, though, share the Frenchman's belief in the consolations provided by art.

La Caze was something of an enigma. The son of a banker, he is thought to have spent time training in the studio of the painter Anne-Louise Girodet, but chose instead to become a doctor. Perhaps the life of an artist seemed too bohemian for him, because demonstrably he had some talent. The Wallace Collection's select exhibition includes a self-portrait by La Caze painted when he was in his mid-forties. Serious, almost stern, his thumb jabbed through a palette, it's hard not to contrast the tightly achieved style with the reality of a man whose taste generally ran to the looser, more expressive brushwork of Jean Antoine Watteau, Jean-Honoré Fragonard and François Boucher.

As is perfectly illustrated by what might well be the star of the show, Watteau's Jupiter et Antiope, an oval-shaped depiction of the god – having first taken the form of a horned and horny satyr – making his move on the recumbent and handily naked nymph. The painting's earthy vitality is expressed both in its form and content, and serves as a mild corrective to those who seek to sanitise the nature of romance.

La Caze, who was never to marry, snapped up the painting just a year before he died for the bargain price of 600 francs. Perhaps it was a case of him mourning opportunities missed.

As well as a couple of Fragonard's expressive portraits de fantaisie, and Boucher's exuberant rendition of Venus in Vulcan's Workshop, complete with Cupid, white doves and some hammering at an anvil, the show also has a more measured undertow, specifically when it comes to the work featured by Jean-Siméon Chardin.

Legend has it that the first painting La Caze ever bought was by Chardin. Of the three on display here, a still life, a portrait of a boy and La Bé*édicité, it is this last, a scene featuring two children and a mother say grace before a meal, that seems most strikingly different, with its appealingly domestic piety.

Certainly, such "realistic" work finds a sympathetic echo in Jusepe di Ribera's painting of a young beggar with a deformed foot. Never mind his deformity, the boy, his hand clutching a permit that allows him to beg, adopts a cheery and dignified pose, baring his less than perfect teeth as he faces an uncertain future. Ribera's work is not unduly sentimental, but recognises his subject as a human being worthy of respect and attention: not always the case in the 17th century, given the unlikelihood of the homeless ever commissioning works of art. While the boy's medical condition may have aroused the curiosity of La Caze, it would also have appealed to the humanity of a philanthropist whose front door was also open to art lovers, historians and painters. Edouard Manet was among those who found inspiration in his art-covered home.

This show's backstory is at least as compelling as the paintings themselves. La Caze seems to have channelled the greater part of his passion and energy, not to mention available finance, into collecting art. Ironically, he was an acquaintance of the 4th Marquess of Hertford, who at that time was himself using his great wealth to acquire the great paintings and other treasures that now constitute the heart of The Wallace Collection. Like a lover of slender means, however, La Caze found a way to get what he wanted. Art was the one true love of his life.

Masterpieces from the Louvre: The Collection of Louis La Caze opens today at The Wallace Collection, London W1 (020-7563 9500), and runs to 8 May